In order to accurately describe the effective mechanical behavior of single-crystalline, austenitic TRIP-steels, a two-phase mean-field homogenization scheme is presented in a finite deformation framework, which also includes transformationinduced eigendeformations. The constitutive behavior of the two phases, namely austenite and martensite, is described by a rate-independent single-crystal plasticity model that captures elastic anisotropy as well as anisotropic slip and hardening behavior. The response of the two-phase model under homogeneous deformation states is investigated and a particle strengthening effect is predicted in the absence of transformation-induced eigendeformations and a suitable choice of material constants, while upon the inclusion of eigendeformations a gradual stress softening is observed.